This kind of messages are a bit unclear. The logic would be understood faster with more explicit messages like "Property cannot be null" or "Wrong value for proprety: null".
https://github.com/matzew/aerogear-unifiedpush-server/blob/0e75417f6d7acad93b413803bf84bf4bd285c1d4/push/sender/src/main/java/org/jboss/aerogear/unifiedpush/message/util/JmsClient.java#L241